1. Field of the Invention
The present invention generally relates to the use and processing of interactive television data for delivering enhanced television programming in a CATV environment.
2. Background Information
The Advanced Television Enhancement Forum (ATVEF) was formed in 1997 by a consortium of 14 leading companies in the television and computing industries. This group developed a public, worldwide specification for creating and delivering interactive TV (ITV) content. In 1999, the ATVEF Specification v1.1, r26 was finalized and published. The ATVEF Specification serves as a standard for creating enhanced, interactive television content and delivering that content to a range of television, set-top, and PC-based receivers. The ATVEF Specification uses existing Internet technologies to deliver enhanced TV programming over both analog and digital video systems using terrestrial, cable, satellite and Internet networks. The ATVEF Specification can be used in both one-way broadcast and two-way video systems, and is designed to be compatible with all international standards for both analog and digital video systems.
Television enhancements are comprised of three related data sources: announcements (delivered via SAP), content (delivered via UHTTP), and triggers (delivered via the trigger protocol over UDP). SAP (Session Announcement Protocol) is a protocol used for session announcements. UHTTP (Unidirectional Hypertext Transfer Protocol) is a simple, robust, one-way resource transfer protocol that is designed to efficiently deliver resource data in a one-way broadcast-only environment. UDP (User Datagram Protocol) is an Internet Standard transport layer connection-less protocol which adds a level of reliability and multiplexing to IP. IP is one of the communication languages used by computers connected to the Internet. This resource transfer protocol is appropriate for Internet Protocol (IP) multicast over a television vertical blanking interval (VBI), IP multicast carried over MPEG, or other unidirectional transport systems. MPEG (Moving Picture Experts Group) is the name of a family of standards used for coding audio-visual information (e.g., movies, video, music) in a digital compressed format. The major advantage of MPEG compared to other video and audio coding formats is that MPEG files are much smaller for the same quality. This is because MPEG uses very sophisticated compression techniques.
In 1953, the NTSC (National Television Standards Committee) developed a set of standard protocols for television (TV) broadcast transmission and reception for use in the United States. An NTSC TV image has 525 horizontal lines per frame (complete screen image). These lines are scanned from left to right, and from top to bottom. Every other line is skipped. Thus, it takes two screen scans to complete a frame, one scan for the odd-numbered horizontal lines, and another scan for the even-numbered lines. Each half-frame screen scan takes approximately 1/60 of a second. A complete frame is scanned every 1/30 second. Each time the electron gun in the television's cathode ray tube finishes scanning a half-frame, it must return to the upper left hand corner of the television screen to prepare for the next half-frame. This takes a significant amount of time, so each pass of the electron gun must be synchronized with the incoming signal. This is done by adding a set of unused lines of data (exactly 21 lines) to the end of each screen scan, giving the electron gun time to return to its starting position. These 21 extra lines make up the VBI. The VBI of a television signal is a non-viewable portion of the television signal that can be used to provide point-to-multipoint IP data services and relieve congestion and traffic in the traditional Internet access networks. IP datagrams may be transmitted using the VBI of a television signal.
Only the first nine lines of the VBI are actually required to reposition the cathode ray. This leaves twelve more lines (10 through 21) that can be used to broadcast data. In the United States, closed captioning data is broadcast on VBI line 21. The transmission of multicast-IP using the North American Basic Teletext Standard (NABTS) is a recognized and industry-supported method of transporting data on the VBI. NABTS has traditionally been used on 525 line television systems such as NTSC.
The ATVEF Specification defines how ATVEF content is displayed and how the receiver is notified of new content. The ATVEF Specification also defines how content is delivered. Since a television or set-top terminal does not necessarily have a connection out to the Internet, the ATVEF Specification describes two distinct models for delivering content. These two content delivery models are commonly referred to as transports, and the two transports defined by ATVEF are referred to as transport type A and transport type B.
Transport type A is defined for ATVEF receivers that maintain a connection (commonly called a back-channel or return path) to the Internet. Transport A is for delivery of triggers by the forward path and the pulling of data by a (required) return path. Generally, this network connection is provided by a dial-up modem, but may be any type of bi-directional access channel. Transport type A is a method for delivering only triggers without additional content. Since there is no content delivered with Transport type A, all data must be obtained over the back-channel, using URLs passed with the triggers as a pointer to the content. ATVEF triggers are broadcast in line 21 of the VBI.
Transport type B provides for delivery of both ATVEF triggers and its associated content via the broadcast network. In this model, the broadcaster pushes content to a receiver, which will store it in the event that the user chooses to view it. Transport B uses announcements sent over the network to associate triggers with content streams. An announcement describes a content stream, and may include information regarding bandwidth, storage requirements, and language (enhancements may be delivered in multiple languages). Transport Type B uses VBI lines 10 through 20 to carry interactive television information, such as IP datagrams.
Thus, with the advent of ATVEF and digital cable TV, a new era in TV viewing experience is emerging in which video complementary data services are available to the TV viewer. There are many potential methods for experiencing these data services. One such way is to use a second display screen on an auxiliary display device. One example of an auxiliary display device is a webpad, which is a relatively small remote wireless device.
Auxiliary display devices are Internet compatible appliances that process and display ATVEF data. The auxiliary display devices are often required to display broadcast television channel video images in a designated area of the screen on the auxiliary display devices. The broadcast television channel video image is normally referred to for obtaining image map data, which defines how ATVEF data and broadcast television channel video images are to be displayed. Under certain circumstances, some auxiliary display devices are unable to access to the video image. Thus, an area of the screen designated for the broadcast television channel video image may not be available for use.